Xerographic development electrode apparatus



XEROGRAPHIC DEVELOPMENT ELECTRODE APPARATUS Filed Feb. 6, 1959 H. O. ULRICH Dec. 5, 1961 4 Sheets-Sheet 1 INVENTOR.

Harold O. Ulrich Dec. 5, 1961 H. o. ULRICH 7 3,011,474

XEROGRAPHIC DEVELOPMENT ELECTRODE APPARATUS Filed Feb. 6, 1959 4 Sheets-Sheet 2 IN VENTOR.

Harold O. Ulrich A TTORNE Y Dec. 5, 1961 H. o. ULRICH XEROGRAPHIC DEVELOPMENT ELECTRODE APPARATUS 4 Sheets-Sheet 3 Filed Feb. 6, 1959 INVENTOR. Harold O. UIrIch ATTORNEY Dec. 5, 1961 H- o. ULRICH 3,011,474

XEROGRAPHIC DEVELOPMENT ELECTRODE APPARATUS Filed Feb. 6, 1959 4 Sheets-Sheet 4 INVENTOR. Harold D. Ulrich A T TORNE Y United States Patent Ofiice 3,011,474 Patented Dec. 5, 1961 3,011,474 XEROGRAPHIC DEVELOPMENT ELECTRODE APPARATUS Harold 0. Ulrich, Los Angeles, Calif. Filed Feb. 6, 1959, Ser. No. 791,570 5 Claims. (Cl. 118-637) This invention relates to an improved development electrode apparatus for the formation of a xerographic powder image on a cylindrical xerographic drum. More specifically, this invention relates to improvements in development electrode apparatus to facilitate the use of such apparatus in automatic xerographic machines.

In the process of xerography, for example, as disclosed in Carlson Patent 2,297,691, issued October 6, 1942, a xerographic plate comprising a layer of photoconductive insulating material on a conductive backing is given a uniform electric charge over its surface and is then exposed to the subject matter to be reproduced, usually by conventional projection techniques. This exposure discharges the plate areas in accordance with the radiation intensity that reaches them, and thereby creates an electrostatic latent image on or in the photoconductive layer. Development of the latent image is effected with an electrostatically charged, finely divided material such as an electroscopic powder that is brought into surface contact with the photoconductive layer and is held thereon electrostatically in a pattern corresponding to the electrostatic latent image. Thereafter, the developed xerographic powder image is usually transferred to a support surface to which it may be fixed by any suitable means.

In a usual line copy form of xerographic development such as black letters on a white background, developer powder is cascaded over the photoconductive plate surface Whereat it adheres to the eelctrostatic latent image with sharpness and uniform density. However, where copy to be reproduced is possessed of images not of line copy form but having instead wide solidly dark areas, the usual cascade development results in the wide areas being black or dark adjacent to their edges and light or white at the central areas owing to the improper and nonuniform adherence of developer powder thereto. This effect is as a result of the linesof force which emanate from the undischarged or image areas being directed in curved paths from the edges or outer portions thereof to the adjacent discharged or background areas effecting a dissipation of force lines from the image area.

When employing a development electrode for xero graphic powder image development, it has been established that the problem of non-uniformity of powder adherence in wide solid image areas is substantially overcome. A form of development electrode is disclosed in Gundlach Patent US. 2,777,418 wherein an electrical field is created between the development electrode and xerographic plate which causes the lines of force emanating from the undischarged or image areas on the photoconductive surface to be directed in generally parallel relation toward the development electrode in perpendicular relationship to the image surface. This results in uniform adherence of the developer powder over the image area and produces a uniformly dark image in the areas desired.

The effectiveness of the fields produced for effecting powder image development increases with a decrease in spacing between the electrode and the plate surface and decreases with an increase in spacing. For equal effectiveness over the entire plate area, the spacing must be uniformly maintained. It has been established that the development electrode is most effective at spacings of less than A" and increasingly effective at spacings of 4;" or less.

Optimum spacing is largely determined by the physical characteristics of the developer powder and means of distributing it between the plate and electrode. Developer powder employed may be a form of two component material such as disclosed in Walkup Patent 2,638,416 wherein the developer powder is comprised of an electroscopic toner powder which is consumed in the developing process combined with a hard granular carrier bead. A form of two component developer powder currently in wide commercial use is manufactured by Haloid Xerox Inc., of Rochester, New York, having carrier beads of which approximately ninety percent vary in dimension between .0176 and .023 inch in diameter. Because the beads are in loose granular form, some piling tends to occur in cascading flow such that spacing therefor between the plate surface and electrode must be sufficiently large to permit gravitational bead passage.

In the aforementioned Gundlach patent a spaced distance between a plate surface and a development electrode of approximately ig is uniformly maintained. However, the apparatus of Gundlach is primarily intended for image development on flat xerographic plates wherein development is effected by hand motivated cascadements of developer powder which usually require several passes in order to assume uniform contact of developer powder with the electrostatic latent image. On a cylindrical drum type xerographic plate of the type employed on automatic xerographic reproduction equipment, a large volume of developer powder is cascaded over the image surface in the direction of drum rotation at a gravitational rate which exceeds the peripheral drum speed. Complete development is effected in a single pass within the developing cycle which usually comprises less than of drum rotation. At minimum rum to electrode spacings excessive amounts of cascading powder unable to effect immediate passage have a tendency to pile up between the electrode and the image surface effecting a block of the gravitational passage. Unless the developer pile-up is prevented by a form of relief or escape, the hard carrier beads of the developer powder caught between the rotating drum surface and the electrode act as an abrasive against the drum, scoring and damaging the relatively soft photoconductive drum surface.

It is therefore a principal object of this invention to improve the construction and arrangement of development electrode means whereby drum damage from excess accumulation of developing powder can be prevented. Since many originals being copied are of line copy form not requiring the application of a development electrode and whereas the need for a development electrode may be intermittently required, it is a further object of this invention to increase the versatility of automatic xerographic equipment by employing the development electrode assembled to the xerographic equipment whereby the electrode can selectively be made effective in close relation to the drum surface or be moved away from the image bearing drum surface to an ineffective position, as required.

These and other objects of the invention are attained by means of an improved development electrode construction wherein the electrode is curved to conform to the curvature of a xerographic drum and is provided with a plurality of slots or openings arranged in a manner to minimize the possibility of pile up of developer material during the developing operation. In addition, means are provided to adjust the position of the development electrode relative to the xerographic drum to place it in an effective or ineffective position, as desired, in accordance with the type or" copy being reproduced.

a development electrode assembly, by reference character 1, that is assembled in an automat- The invention is shown in the accompanying drawings, in which:

FIG. 1 is a schematic side elevation of an automatic xerographic reproduction apparatus in conjunction with the development electrode of the invention;

FIG. 2 is an isometric view of the development electrode of the invention in operative relation to a xerographic drum;

FIG. 3 is a sectional view taken substantially on the line 3-3 of FIG. 2;

FIGS. 4 and 5 illustrate alternative structures for assembling the development electrode of the invention in relation to a xerographic drum;

FIG. 6 is a wiring diagram; and

'FIG. 7 illustrates a typical slot pattern for the conducting plate of the invention.

Referring to the drawings, the-re is illustrated in FIG. 1 enerally designated ic xerographic equipment 2 which includes components for effecting the xerographic process consisting of an opaque original exposure means 13 and/ or a microfilm exposure means 14, either of which may be employed to effect exposure of an original to be reproduced onto a rotating xerographic plate or drum 15 bearing a uniform electrostatic charge on its photoconductive surface 28 ap-' plied thereon by electrostatic charging unit 16. Exposure of the original to be reproduced forms an electrostatic latent image on or in the photoconductive surfaceZd, which is subsequently developed into a 'xerographic powder image by developing unit 17. After development,

paper handling mechanism 18 transports a paper support 19 onto contact with a xerographic powder'image on surface 28 which is transferred to support surface 19 by electrostatic attraction applied from electrostatic charging unit 20. Mechanism 15 continues transport of support surface 19 until the xerographic powder image thereon passes through heat fuser 21 wherein the powdered image is aifixed to support surface 19. After transfer, residual powder on drum 28 is removed by brush cleaners 213.

More specifically, drum 15, consisting of a photoconduc- Y tive surface 28 on an electrically conductive backing, 29 is driven at a constant rate of rotation by motor 12. After I an electrostatic charge is applied to surface '28 by charging unit 16, which may be of a type disclosed in Walkup US. Patent 2,777,957, an opaque original to be reproduced may be exposed to photoconductive surface 28 by exposure means 13 which may be of a type disclosed in copending application Serial No. 837,173, filed August 31, 1955 in the name of A. Cerasani et al. When employing exposure means 13, an opaque original may be exposed at variable magnification ratios onto surface 28 by feeding an original from tray 27 onto moving belts 26 whereat belt movement is effected by motor '31? through variable speed transmission 31 which drives roller 32 engaging belts 26. Passing below glass plate 33, an original is illuminated by lamp 39, and the image thereon is reflected to mirror 40 wherefrom it is caused to be reflected through the optical axis of lens '41 to mirror 42 thence through variable exposure means 43 normally onto surface 28. Variable magnification of an opaque original to be reproduced is effected by proper correlation of transmission speed from transmission 31 through adjustment of rotatable knob 48, accurate positioning of lens 41 through adjustment of rotatable knob 49, and effecting a required length of the optical path emanating below glass plate 33 to surface 28 by rotatable adjustment of handw-heel 511.

In the alternative, microfilm originals to be reproduced can be projected from microfilm 56 onto photoconductive surface 28 by microfilm projection apparatus 14 which may be of a type of microfilm projection apparatus disclosed in copending application Serial No. 796,561, filed March 2, 1959, in the name of S. R. Johanson. When employing apparatus 14, microfilm originals are transported from supply spool 57 onto take-up spool 58 by motor and variable speed transmission means (not shown). While in transport, microfilm is caused to transport through an optical path normal to surface 28 Whereat the image is illuminated by lamp 59 and projected by a lens 60,- 61 or 62, through variable exposure means 43 onto photoconductive surface 28; mirror42 being moved to a vertical position by control rod 44 so as not to obstruct the optical path. Lenses 60, 61 and 62 are lenses of different focal lengths and areeach secured to rotatable turret 63 whereby projection of microfilm onto surface 28 may be effected at variable magnification ratios by selectively aligning and adjusting the appropriate lens into the optical path, effecting correlation of film transport speed to drum speed through motor speed and transmission speed selector switches 79 and 71, respectively, and effecting the proper spaced distance in the optical path between microfilm '56 and surface 28 through the rotation of adjustment knob 72.

Thereafter, development of the electrostatic latent image al., wherein a continuously operative conveyor '79 driven by motor 89 scoops developer powder 81 from the bottom of housing 82 wherefrom it is conveyed to the top of 82 and dumped into hopper 83. Gate 84-, positioned by motor 85, is either open or closed dependent upon whether the xerographic apparatus is on or off respectively and when open permits powder 81 to cascade over rotating surface 255 and below development electrode assembly 1 wherefrom it gravitates through chute 86 having a top wall 99 and side walls 91 and 94 which cooperate with the drum to form asubst-antially powder tight passage therebetween. From chute 86 the powder gravitatcs to chute 87 wherein it is returned to the bottom of housing 82. is maintained in hopper 83 by overflow chute 88. As the toner componentof the developer powder is consumed turning in chute 87.

For elfecting development of wide solid areas of image as aforesaid, development electrode assembly includes (refcralso FIGS. 2, 3 and 6) a potential of approximately 60-90 volts supplied from batteries 95 housed in battery case 96 and wired therefrom by lead 97 to clip 98 electrically secured to conducting plate 112. In developing a positive print of a positive original it is the usual practice to employ a negatively charged electroscopic powder which is attracted to the positive image on the xerographic plate and for which a development electrode biasing voltage of 6090 volts has been found satisfactory. However, in a reversal form of development, that is, in a negative original to a positive print it is the usual practice to employ a positive electroscopic powder which is repelled by the charged non-image areas on the plate and in this instance a development electrode biasing voltage of approximately 500 volts is preferred.

T-sha-ped support bar 111 is secured from the top wall of 911 of chute 86 by several screws 111. Conducting plate 112 is secured by clips 113 to insulating side bars 114- and 115 which are braced in fixed relation by support members 116 and 117. Ball-knob 122 is secured to vertical shaft 123 which has a positioning groove 125 and a shoulder 126 seated on the top side of support member 117. Nut 127 serves to maintain 117 in firm engagement against shoulder 126.

In FIG. 3 the comparative spaced relation of conducting plate 112 is illustrated for both effective and ineffective positions of the development electrode assembly wherein the 112 dashed outline represents the inelfective position of conducting plate 112 and the solid outline in close relationship to surface 23 represents the effective position to A maximum level of developer powder effect spacings between the electrode and drum surface of A2" to 5 which have shown to give optimum development results without damaging the drum surface. In effective position in a preferred embodiment of the invention the inherent weight of the electrode apparatus maintains conducting plate 112 in close relationship to surface 28 with its forward position (as viewed in the direction of drum rotation) aligned by nuts 131 and 132 secured to bolt 134 with nut 133 serving as a lock nut. The rearward position of conducting plate 112 is adjustably obtained by socket head bolts 135 and 136 having their socket ends inserted upward into each of counterbores 139 of side bars 115 and 114 respectively, and their threaded ends secured by nuts 137 and 138, respectively. For securing the development electrode in ineffective position, clip 1 44 is slidably secured to the horizontal surface of support bar 110 whereby its lip 145 can be made to engage or disengage groove 125 when in upper position. When clip 144 is slid out as to disengage 125-, shaft 123 is freely movable vertically whereby conducting plate 112 can be moved toward or away from surface 28 into effective or ineffective relation, respectively. Thus, by raising or lowering the development electrode it can selectively be applied to the developing cycle when required to attain the desired development effects obtainable thereby.

To provide relief from developer pileup so as to prevent drum scoring, conducting plate 112 includes a plurality of elongated slots or openings 149 whereby drum motion forces excess developer to ascend through slots 149 whereat it continues gravitationally to cascade over the top of 112 seeking a slot whereat it can descend onto surface 28. In the arrangement shown openings 149' are approximately 7 wide but of width preferably greater than three bead diameters. In addition, the slot ends are semicircular and the slots are approximately in length to the extremities, and are spaced approximately on center in direction of drum width. Although openings 149 may advantageously be formed in the manner defined, it is obvious thatthe particular configuration of the openings is not critical to the proper functioning of the apparatus of the invention. Openings 149 may be made and spaced in any of a variety of configurations. The only known limitations are that they should be arranged in -a manner to permit pileup relief over the entire developing area, and that the minimum dimension of the openings should be greater than three diameters of the developing material carrier.

By the arrangement of preferred development electrode assembly described, wherein a uniform spaced relation is maintained by the inherent weight of the electrode, in addition to pileup relief aiforded by the elongated slots 149, relief to a lesser degree is effected by excess developer urging the conducting plate 112 away from surface 28 whereafter its weight restores the relation.

Typical alternative structures embodying the invention are shown in FIGS. 4 and 5 wherein FIG. 4 illustrates substantially the same development electrode assembly described in the preferred embodiment of FIGS. 2 and 3, but in addition thereto four wheel type followers 153, two on each side of bars 114 and 115, are each secured to a pin 154 which is rotatably secured in turn to suitable bearing means (not shown) of adjustable support bracket 155, which by screw 156 through slot 157, are secured to insulated side bars 114 and 115. Resilient spring means 158, on opposite sides of assembly 1, encircling pins 159 and secured between support member 117 and the top wall 90, urge each of the followers toward the drum such that the spacing between the drum and conducting plate 112 as elfected by the setting of adjustable brackets 155 is maintained against any eccentricity of surface 23 as may be encountered in drum rotation.

In FIG. 5, a slightly different geometric configuration at the ends of conducting plate 112 is indicated, but in all other respects is substantially similar to that previously described. Conducting plate 112 is secured with screws 162 to insulating bar 167 in turn secured with screws 163 to horizontal support members 168 which is secured with screw and nut assembly 194 to pivot member 169. Pivot member 170, secured to support plate 17 1, supports rotatable pin 172 to which pivot member 169 is secured. Support plate 171 is secured to the top wall through screws 1'73 and brackets 17 4. Compressed spring 17 8 encircles shaft 123 and is secured between plate 179 and swivel seat 180, seat 181 being secured to pin 181 which is rotatably secured between parallel legs of bracket 182 in turn secured to support member 168. Two wheelfollowers 183 on opposite sides of plates 112 are each secured to a pin 1 34 which are rotatably secured in suitable bearing means (not shown) of a support bracket 185 which is adjustably secured through slot 188 to a brace 186 by screw and nut assembly 187. Brace 186 is secured to conducting plate 112 by screw and nut assembly 191 being electrically insulated from conducting plate 112 by insulator washers 192 and 193. Alignment of 112, in relation to surface 28, is achieved at the forward end (as viewed in direction of drum rotation) by the position at which screw and nut assembly 194 is secured through slot 195 of 16? and at the rearward end by the adjusted position of brackets 1 85 in relation to 186. With development electrode assembly 1 in effective relation as shown in FIG. 5, wheel followers 183 are maintained in contact with conducting surface 29 by the urging resilient action of spring 178. Lifting of ball knob 122, against the urging force of 178 causes the assembly to pivot about pin 172 where ultimately shaft 123 can be secured in uppermost position by latching clip 144- to seat in groove 125.

In operation, with drum 15 in constant rotation and all the components of the xerographic reproduction apparatus operative, it is first determined whether the opaque original or the microfilm original to be reproduced is of a form for which a development electrode assembly is properly applicable, that is, whether the original is a straight line-copy form reproduction, or whether the original to be copied possesses wide solid image areas which can be developed in accurate duplication only by employing a development electrode assembly. Having determined that the development electrode can be effectively utilized for the original to be reproduced, in the preferred arrangement, clip 144 is first slid out so as not to engage groove 125 whereon ball knob 122 can be lowered so as to place conducting plate 112 in effective spaced relation to rotating surface 28. After an electrostatic latent image is formed on charged surface 28 by exposing an original to be reproduced thereto by means of unit 13 or 14, the latent image thus formed rotates into contact with developer powder 81 cascading from hopper 83. Developer powder continues to cascade between conductor plate 112 and surface 28 until falling away from surface 28 into chute 87. In the event a pileup of developer powder should occur between surface 28 and conducting plate 112 as a result of being unable to gravitate freely therebetween, the excess powder ascends through one of the many perforated slots 149 of conducting plate 112 wherefrom it continues to cascade to the top of 112 until descending through a slot opening past the pileup onto surface 28. Development electrode assembly 1 can be left in place for successive and subsequent developments, or if subsequent developments are not of the form wherein a development electrode can be beneficially applied, it can be rendered ineffective by lifting ball knob 122 until lip 145 of clip 144 can be inserted into groove 125, thereby to secure conducting plate 112 in ineffective relation.

Thus, there has been described a development electrode apparatus to be employed in conjunction with development of a xero graphic powder image on a cylindrical xerographic drum whereby the development electrode is movable such that it can selectively be rendered effective or ineifective in relation to development of a xerographic powder image, and whereby in effective relation, a uniform close spacing of the development electrode to the drum surface is maintainable which saves the photoconductive drum surface harmless from the effects of excess developer powder accumulation.

Since many changes could be made in the above construction and many apparently widely different embodiments could be made without departing from the scope thereof, it is intended that all matter contained in the drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a xerographic developing apparatus for developing an electrostatic latent image on the surface of a cylin drical xerographic drum having a photoconductive layer on a conductive backing wherein a development electrode is arranged in closely spaced relation to a portion of the surface of said xerographic drum and is arranged in an electrical circuit to establish an electrical field between the development electrode and the drum and wherein development of said electrostatic latent image is effected by cascading developing material between said drum surface and the development electrode, said developing material including a component having a dimension such that binding of developing material particles can occur; the improvement which comprises a development electrode having a plurality of openings throughout its area whereby excess developing material may pass through said openings and away from said drum surface.

2. In a Xerographic developing apparatus for developing an electrostatic latent image on the surface of a cylindrical Xerographic drum having a photoconductive layer on a conductive backing wherein a development electrode is arranged in closely spaced relation to a portion of the surface of said xerographic drum and is arranged in an electrical circuit to establish an electrical field between the development electrode and the drum and wherein development of said electrostatic latent imag is effected by cascading developing material between said drum surface and the'development electrode, said developing material including carrier beads of a dimension such that binding of carrier beads can occur; the improvement which comprises a development electrode having a plurality of perforations throughout its area, said perforations having a minimum dimension greater than three carrier bead diameters whereby excess developing material may pass through said perforations and away from said drum surface.

3. In a xerographic developing apparatus for developing an electrostatic latent image on the surface of a cylindrical Xerographic drum having a photoconductive layer on a conductive backing wherein a development electrode is arranged in spaced relation to a portion of the ably settable mounting means for the development electrode which includes means to place said development electrode into closely spaced relation with said drum surface or to place said development electrode into ineffective spaced relation therewith.

4. In a xerographic developing apparatus for developing an electrostatic latent image on the surface of a cylindrical Xerographic drum having a photoconductive layer on a conductive backing wherein a development electrode is arranged in closely spaced relation to a portion of the surface of said xerographic drum and is arranged in an electrical circuit to establish an electrical field between the development electrode and the drum and wherein development of said electrostatic latent image is effected by cascading developing material between said drum surface and the development electrode, said developing material including carrier beads of a dimension such that binding of carrier beads between the drum surface and the development electrode can occur, the. improvement which comprises a development electrode having a plurality of perforations throughout its area, said perforations having a minimum dimension greater than three carrier bead diameters, a follower means secured thereto and extending therefrom toward said drum surface, and resilient means urging said follower means into contact against said surface whereby effective spaced relation between said development electrode and said drum surface is uniformly maintained.

5. An apparatus for developing line-copy or solid-area electrostatic latent images on the. surface of a xerographic plate, said apparatus including a xerographic plate. in the form of a cylindrical drum, means to cascade developing material over the image-bearing drum surface, a developsurface of said Xerographic drum and is arranged in an ment electrode formed to conform to and overlie a portion of the drum surface over which developing material is cascaded, wherein the developing material includes a component having a dimension such that binding of developing material particles between the drum surface and the development electrode can occur, and wherein the development electrode is provided with a plurality of openings throughout its area whereby excess developing material may pass through, said drum and said development electrode being connected in an electrical circuit to establish an electrical field therebetween, support means to support the development electrode in spaced relation to said drum surface portion, and selectively settable means connected to the support means to position the support means either in a first position in which the'development electrode is in closely spaced relation to said drum surface portion, whereby the electrical field therebetween is effective to effect image development, or in a second position in which the development electrode is further removed from. the drum surface, whereby electrostatic latent images on said drum surface are developed independently of said development electrode.

References Qited in the file of this patent UNITED STATES PATENTS 7 2,573,881 Walkup et al Nov. 6, 1951 2,777,418 Gundlach Jan. 15, '1957 2,808,177 Lowrie Aug. 20, 1957 2,831,409 Bixby et a1. Apr. 22, 1958 2,877,132 Matthews Mar. 10, 1959 2,911,944 Hayford et al. Nov. 10, 1959 

